The Drizit thought the world they invaded was ripe for the picking because the inhabitants had no obvious weapons. They thought that an agrarian culture was passive and harmless. They should have really done their homework, because these apparently passive agrarians were also humans.

They took precautions, because parasitising an entire planet largely depends on remaining undetected until your presence is merely a fact of life. They took steps like burrowing into normally inaccessible areas, only stealing when the local populations were seemingly inactive, utilising the best of their stealth technology and so forth.

They didn't reckon with Humans who invented things like Duck Blinds, Night Vision Goggles, and occupations like Owl Tagging. The residents of a planet called Meggidio knew about the Drizit in less than a week. Following that, it was merely the process of tracking them down that allowed the Drizit to persist for as long as they did.